Very simple piezo trigger/gain amp

creatorlars

I just bought an Emu Drumulator, which has 4 gate inputs to fire the drum sounds. The gate inputs are functioning great when triggered with a gate signal from my synth or sequencer. However, my Piezo-based drum trigger pads are not producing a voltage level high enough to trigger the drum -- Unless I strike them very hard.

I need to rig together a very last minute circuit to boost the sensitivity and gain on 4 incoming Piezo triggers before they get to the Drumulator. I am assuming this would be something extremely simple, like a quad op-amp, four sensitivity pots, and a handful of resistors.

I am familiar with some gate-to-trigger and Thomas Henry's Trigger conditioner circuits, however I don't even need this much functionality -- just something simple and probably battery powered in a breakout box.

Ideas on where to look? Possible problems with the idea?

Coriolis · Joined: Apr 11, 2005 Posts: 616 Location: Stilling, Denmark

I was just about to suggest those TH circuits - I wonder if they get much simpler than that?

C

creatorlars · Posted: Tue Jul 29, 2008 1:05 pm Post subject:

Maybe not... the TH "Trigger Conditioner" doesn't have a sensitivity level pot, though. His "Piezo Drum Pad" seems to. Really i just need a way to boost the level of the piezo signal, no need to condition the trigger or anything.

Coriolis · Joined: Apr 11, 2005 Posts: 616 Location: Stilling, Denmark

Funky40 · Posted: Tue Jul 29, 2008 4:39 pm Post subject:

if you just wanna trigger then i think you need a comparator circuit.
this is the Circuit serenadi, a Friend of mine has used in the past.
"comparator with adjustable threashold".
maybe look at wikipeda or other places for more infos about comparators.
I have never bult one myself
edit: had to change the attachment, this one is what i meant

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Joel · Joined: Sep 12, 2006 Posts: 97 Location: London, UK

strangely I was just looking this up! Here's a link to an old PAIA page on percussion sensors - the page has been deleted so the link uses the internet archive :

http://web.archive.org/web/20030608211101/http://www.paia.com/drumsens.htm

hope this helps! Joel

creatorlars · Posted: Wed Jul 30, 2008 6:54 am Post subject:

Awesome! I think that comparator schematic is exactly what I need, for something this simple. If it has trouble triggering, I'll add in a trigger conditioning circuit. Thanks so much for the info, I'll let you know how it goes!

Funky40 · Posted: Wed Jul 30, 2008 9:22 am Post subject:

Yes please, let us know !
I'm very interested in piezo triggers too

creatorlars · Posted: Thu Jul 31, 2008 7:23 am Post subject:

Should any op-amp theoretically be able to be used in that comparator schematic? I tried it last night with a TL084 but was having some problems. I know Thomas Henry's circuit is a 741. Can the op-amp's positive and negative power pins be connected to +V and Ground, or do I have to have a dual polarity supply for this? I was hoping to just use a 9V battery.

richardc64 · Posted: Thu Jul 31, 2008 10:25 am Post subject:

Theoretically any op amp can be used for a comparator (despite what some may say,) but not easily with a single supply. Try the pAia circuit, which has not been deleted, but merely moved.

http://paia.com/ProdArticles/drumsens.htm

For piezos you won't need R2 and C3.

creatorlars · Posted: Thu Jul 31, 2008 11:36 am Post subject:

Cool -- I've bought the components to build the PAiA and thomas henry circuits.

It looks like I can piece together something that will work from a combination of these.

My concern with the PAiA circuit -- is that meant to deliver a 0-5v range? Or a 5v trigger pulse?

richardc64 · Posted: Thu Jul 31, 2008 2:32 pm Post subject:

In the PAiA circuit, the LM324 is a voltage follower, so the output(s) could get as high as whatever voltage the LM324 is powered with, depending on the input voltage -- that is, how hard you strike the pad. If all you need is 5v, power it with 5v.

For a quad, single-supply comparator look up the LM339.